STATIC AND FREQUENCY-DEPENDENT POLARIZABILITIES OF EXCITED SINGLET-STATES USING COUPLED-CLUSTER RESPONSE THEORY

We report an implementation of the linear response function for single t excited states for the coupled cluster models CCS, CC2 and CCSD. The implementation is based on the derivation of excited state response f unctions as derivatives of excited state quasienergy Lagrangians. Secu lar divergencies are explicitly eliminated and response equations and response functions therefore are numerical stable in the static limit. Calculations are performed for the polarizabilities of pyrimidine and s-tetrazine in their lowest singlet excited states. We find that the results for the excited state polarizabilities are sensitive to the ac curacy of the excitation energies and that a qualitative correct descr iption of the dispersion is first obtained at a correlated level. (C) 1998 American Institute of Physics. [S0021-9606(98)31244-1].